Methods for making fiberglass reinforced plastic (FRP) panels are taught in U.S. Pat. Nos. 4,329,194; 4,504,343; and 4,568,593, which are incorporated herein by reference.
According to the '343 patent, for example, a composite laminate can be formed by applying resin between layers of backing webs and webs of transverse unidirectional filaments. The laminate is fabricated by pulling fiberglass webs off rollers in a continuous sheet, which is wetted with resin. This mixture is trapped between two plastic films that allow the material to be handled. Once trapped between the two films the material is drawn into a massive oven, which may exceed 50 feet or more, where it is shaped and cured to produce the finished composite member. The large oven permits the panel line to be moved continuously past the heating units. Near the entrance of the oven, molds or shapers, such as shown in FIG. 2 of the '194 patent, bend the laminate into a corrugated shape. The cured panel exits the oven, where the two plastic films are removed, then the panel is advanced by tractor units to a saw, where the panels are cut into desired lengths.
The assessment of the state of resin cure in corrugated fiberglass panels has been typically manually controlled. The speed of the line is critical because it determines how much heat is added to the panel to promote the cure. The manual control of the speed requires constant vigilence by an experienced and diligent operator who must examine and feel the moving panel through various openings along the length of the oven to assess the state of cure. Moreover, the panel must cure in a specific spot in the oven: if the resin-wetted laminate is too soft, it gets snagged, torn, and/or mutilated at any number of stages; if the laminate is prematurely hardened, the desired shape is not obtained. Errors generate costly scrap material.
U.S. Pat. Nos. 3,722,462; 3,762,896; 3,845,287; and 3,989,934 disclose automated continuous line production apparatuses for controlling oven temperature and/or the extent to which fibers or webs that move through the oven are impregnated or coated.
In view of the foregoing disadvantages of the prior art, what is needed is a highly accurate system and method for controlling FRP panel line production.